Efficient polymer‐mediated delivery system for thiocyclam: Nanometerization remarkably improves the bioactivity toward green peach aphids

Abstract

The unscientific application of synthetic pesticides has brought various negative effects on the environment, hindering the sustainable development of agriculture. Nanoparticles can be applied as carriers to improve pesticide delivery, showing great potential in the development of pesticide formulation in recent years. Herein, a star polymer (SPc) was constructed as an efficient pesticide nanocarrier/adjuvant that could spontaneously assemble with thiocyclam or monosultap into a complex, through hydrophobic association and hydrogen bonding, respectively, with the pesticide-loading contents of 42.54% and 19.3%. This complexation reduced the particle sizes of thiocyclam from 543.54 to 52.74 nm for pure thiocyclam, and 3 814.16 to 1 185.89 nm for commercial preparation (cp) of thiocyclam. Interestingly, the introduction of SPc decreased the contact angles of both pure and cp thiocyclam on plant leaves, and increased the plant uptake of cp thiocyclam to 2.4-1.9 times of that without SPc. Meanwhile, the SPc could promote the bioactivity of pure/cp thiocyclam against green peach aphids through leaf dipping method and root application. For leaf dipping method, the 50% lethal concentration decreased from 0.532 to 0.221 g/L after the complexation of pure thiocyclam with SPc, and that decreased from 0.390 to 0.251 g/L for cp thiocyclam. SPc seems a promising adjuvant for nanometerization of both pure and cp insecticides, which is beneficial for improving the delivery efficiency and utilization rate of pesticides.

A Preparation Method of Nano-Pesticide Improves the Selective Toxicity toward Natural Enemies

“…Our results revealed that there was a strong hydrogen bonding and Van der Waals forces between CNAP and SPc, and we deduced the amide NH of CNAP and carbonyl groups or tertiary amines of SPc played an important role in the self-assembly of CNAP/SPc complex. Consistent with previous studies, the SPc can assemble with dinotefuran, monosultap, avermectin and chitosan through hydrogen bond and Van der Waals forces [ 25 , 32 , 33 , 57 ]. Meanwhile, the SPc can also combine with thiocyclam, eugenol, thiamethoxam, matrine and osthole through different interaction forces, such as electrostatic interaction and hydrophobic association [ 25 , 29 , 30 , 31 , 33 ].…”

“…As a gene/pesticide nanocarrier, the SPc can be complexed with various exogenous substances for enhanced delivery and bioactivity [ 24 , 25 , 29 , 30 ]. The current study illustrated that the pesticide loading content of SPc toward CNAP was 24.79%, which was higher than those of osthole (17.09%), thiamethoxam (20.63%), monosultap (19.3%), and dinotefuran (17.41%) [ 30 , 31 , 32 , 33 ]. The binding affinity of CNAP with SPc was then analyzed using a high-accuracy method ITC [ 54 , 55 ].…”

“…Similar to previous studies, the LC 50 values of osthole decrease from 49 to 34 mg/L toward green peach aphids and from 332 to 270 mg/L toward two-spotted spider mites with the help of SPc [ 30 ]. Furthermore, with the help of SPc, the LC 50 value of pure thiocyclam decreases from 532 to 221 mg/L toward green peach aphids [ 33 ]. The potential mechanism of enhanced contact toxicity may be the CNAP nanometerization by the nano-delivery system, which leads to enlarged contact area to target pests and improved penetration across the insect cuticle.…”

“…The loading capacity of SPc toward CNAP was measured using the freeze-drying method according to the method described by Wang et al [ 33 ]. The 100 mg of CNAP and SPc were dissolved in 25 mL of methanol and 75 mL of double-distilled water (ddH 2 O), respectively.…”

“…The SPc-loaded cargo can be efficiently delivered across the plant/insect cell membrane by activating the clathrin-mediated endocytosis [ 24 , 25 , 26 , 27 , 28 ]. Based on the current publications, the SPc can assemble with several pesticides, such as matrine, osthole and thiamethoxam to form nano-sized pesticides for improved bioactivity, enhanced plant uptake and reduced pesticide residue [ 29 , 30 , 31 , 32 , 33 ]. Thus, the SPc-loaded pesticides have the potential to overcome agricultural, forestry and environmental challenges.…”